MySpace was once the default social network but then Facebook sent it into obscurity.
MySpace is the prime example of an early adopter that blew a big lead. Their failure to innovate and keep up with the evolving technology allowed Facebook to take over. So it can be done, but Facebook probably benefited from MySpace’s stupidity in order to pull it off. Once Facebook achieved a critical mass they were able to use the network effect against MySpace. There’s really not room for more than one big dog in these internet spheres.
Also see: Altavista